PROJECT SUMMARY Proper turnover of adult tissues requires that stem cells carefully regulate both their division rates and fate outcomes to maintain tissue homeostasis. Loss of proper division rates and fates is a hallmark of cancer; therefore, understanding how these two processes are linked is vital to our understanding of how to prevent and treat this disease. Previous research suggests an intimate link between the cell cycle and fate outcomes; however, current work exploring this link between cell cycling and fates focuses primarily on embryonic stem cells and adult stem cells in culture. Thus, little is known about how cell cycle kinetics regulate adult stem cell fates in vivo. My long-term goal is to understand the mechanisms underlying cell cycle regulation of adult stem cell fates and how the coupling of these two processes drives homeostasis and controlled tissue growth. Towards this goal, I will probe how the duration of the cell cycle gap phases G1 and G2 regulate adult stem cell fates. The adult Drosophila midgut is a uniquely suited model for studying this question because of the live imaging protocol our lab has pioneered, and the versatility of available genetic tools such as the dynamic, reporter of cell cycle progression (Fly-FUCCI). Combined with a novel image analysis workflow I developed to quantitatively report population-level cell cycle progression, I can visualize and quantify the dynamics of cell cycle progression and fates in vivo. I will investigate three fundamental questions concerning the role of cell cycle progression in adult stem cell fates. First I will determine whether stem-cell specific perturbations in G1 or G2 duration impact fate outcomes of adult stem cells using lineage tracing. Second, I will explore the mechanism by which G1 or G2 duration may regulate the ability of newborn daughter cells to send or receive fate-determining Notch signals. These experiments will be achieved using a combination of clonal analysis and live imaging of Notch pathway components and reporters of Notch activity. Third, by using my quantitative analysis techniques and lineage tracing, I will investigate whether the growth factors Insulin and EGF regulate G1 or G2 duration on a tissue- wide scale to drive the cell cycle progression and fate changes observed between growth and homeostasis. This proposal lays out a highly interdisciplinary training plan by combining microscopy techniques in fixed tissue and live imaging, Drosophila genetics, and techniques in quantitative image analysis. Altogether the proposed work will provide novel insight into cell cycle regulation of adult stem cell fates in vivo to drive complex tissue dynamics such as homeostasis and controlled tissue growth.